I've read the neck tension statement before. I need to understand what it means. Do you think the brass too "springy" for a taper crimp to establish neck tension?

Also, I need to understand something else. Why do you say that an auto cartridge's headspace is "based" on extractor tension holding the cartridge against the breech face. Headspace is a dimension, staying with auto pistols, measured from the breech face to the case mouth "step" in the barrel, with the breech in battery. Isn't it?

I mean if your extractor broke, you could still safely fire a round in a properly headspaced chamber, couldn't you? You wouldn't be able to extract a case, but headspace would still be within specs. What has the extractor got to do with headspace?

Hypothetical question using a .45 ACP: If your case rim is .049, the extractor hook contact face is .056 off the breech face, the case is .898 long (head-to-mouth), and the in-battery chamber length is .902, then even if the case is fully forward in the chamber, the extractor won't be back against the rim.

2) Auto cartridges headspace based on extractor tension holding the cartridge against the breech face.

3) Measuring at the case mouth, 40 S&W should go around .422".

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Point 1 is correct to a degree, point 2 is not.

And I see that I brain farted and said that a semi-auto case should headspace on the rim. I'm too used to shooting revolvers.

With the majority of semi-autos, that is not the true, the case headspaces on the casemouth. Old .38 ACPs and .38 Supers used to use the "rim" for headspacing, but it was so small that it caused lots of problems. Modern .38 Supers headspace on the case mouth.

And, of course, the shouldered rounds like the .357 Sig. headspace on the shoulder.

A properly headspaced, straight walled semi-auto case headspaces on the case mouth, which is why loading manuals state that you should not use a roll-crimp with semi-auto cases. In an extreme case, the extractor may never snap over the rim of the case as the round chambers. If the crimp is excessive the round can drop deeply enough into the chamber that the firing pin won't ignite it. I've seen that more than once with newbie reloaders, and those who use, say, a .357 Mag. die with a roll crimp to crimp .38 Super rounds.

Crimp is where the case mouth is physically pushed aginst the cannelure or crimp groove to prevent the bullet from moving in or out.

Neck tension is the portion of the case pushing against the seated area of the bullet (the portion of the bullet inside the case) to prevent the bullet from (in an extreme example) wobbling to and fro.

Neck tension is what you get from sitting to close to the screen in the movie theater.

Crimp is what your girlfriend does to your style...

Ok... All levity aside... Here are my definitions...

Neck tension.

This is the degree to which the brass will hold the bullet after the case has been full-length sized.

Full length sizing returns the case to "correct factory" dimensions. A lot of things can mess with neck tension...

Springy brass. Brass is elastic, and has a rebound effect. After you size it, it bounces back to a certain degree. As brass is reused, it gets work hardened, meaning that it won't spring back nearly as much as when it was new. Annealing will restore the ability of the brass to spring back.

Expander ball size. An oversized expander ball will give you fits every time. I've seen a couple over the years.

Brass that is too thin. This can be a particular problem with foreign 9mm Para. and .38 Spl. brass, but also with other calibers, as well. If the brass is too thin, it's the equivelent of having a sloppy sizing die or an oversized expander ball.

Weshoot is correct in saying that you need proper neck tension in order to keep the bullet in place. Unless you using a hard roll crimp that gets down into the crimping groove , crimp alone won't be successful in keep the bullet from moving if neck tension isn't adequate.

In a semi-auto pistol when the firing pin comes forward and strikes the primer, usually the case is going to move forward a bit. Something stops the case from going too far into the chamber. This can be the extractor contacting the rim, or the case mouth contacting the front of the chamber.

Given manufacturing tolerances, and chambers that are cut large for functioning, the extractor is usually the "thing" that stops the round.

Is that round "headspacing" on the case mouth or the extractor?!?

When I shoot my 1911 I say the it headspaces on the extractor. Same rounds in my Blackhawk convertible headspace on the case mouth. Same rounds in my 625-3 headspace on the full moon clip.

It's probably a mater of how a person defines/understands "headspace", but I think WESHOOT2 is correct in his statement.

The extractor will prevent the cartridge from traveling too far forward in the chamber, as the slide returns to battery, and that can prevent a catastrophic rearward acceleration of the brass at firing, BUT ... if the extractor is worn and the cartridge is allowed to travel forward far enough in a loose (let's say slightly over SAMMI max chamber), then the rearward motion of the brass precedes that of the forward motion of the bullet (less mass). More chamber space, more brass travel rearward prior to bullet engagement of rifling. Accuracy suffers, HOT gasses pass the bullet into the barrel, HOT gasses escape around the brass (because it doesn't expand rapidly, BECAUSE it is moving to the rear), recoil operation is not reliable, pressure pulse is OUTSIDE the brass in the chamber ...YIKES! Anyone have an airtight chamber? I didn't think so.

Now, my example is exaggerated, because I cite an extractor worn beyond belief and a chamber way too long. The point is: the cartridge HEADSPACES on the CASEMOUTH. PERIOD! Headspace is the maximum allowable chamber length, in battery, measured from case head to some repeatable point of measure and case contact with the chamber.

.30-30 (rimmed) lever actions have extractors. .30-'06 (rimless) bolt actions have extractors. .223 (rimless) autos have extractors. Single shot .38-55 Ballards (rimmed) have extractors. NONE of them headspace on the extractor! How did this fiction begin?

As for neck tension ... all crimps are not equal. Neck tension is primarily established during withdrawal of the expander ball. The taper in a taper crimp is very slight. A taper crimp re-establishes neck tension lost from belling the mouth and overlarge expander balls and establishes uniform case contact with the bullet so it will not travel past the headspace "ledge" at the front of the chamber. It does not roll the case mouth at all, cannelure or not.

Wanna find out what barrel makers consider headsapce to be? Call Brownell's. Better yet call Clymer. They make reamers. Ask them if headspace depends on "how a person defines/understands "headspace"".

One more question. What is that little ledge in a .45 ACP's or a .40 S&W's barrel for anyway? I'll tell you. It's to stop the case mouth from moving into the barrel. It's the end of the chamber. For straight-walled, rimless cases, it's one end of the measurement of the headspace dimension. The other end is the breech face, in battery.

Kframe19 is right in what is "supposed" to happen, the design specs say that auto cases headspace off of the case mouth.
If you measure your cases, you will see that they are usually too short to headspace properly. .45 ACP cases are supposed to be .895" long, with a chamber depth of .898"; for a headspace of .003". Most 1911 auto pistols work just fine with cases as short as .850"; giving a headspace of .048". The extractor holds the too short case against the impact of the firing pin and the cartridge fires, instead of just sliding up into the chamber. I gave the dimensions of the .45 ACP, but it works just the same with 40 S&W, 10 mm etc.
The 9 X 19 is actually supposed to be a tapered case (.392 case head, .380 case mouth), but is typically reloaded with carbide dies that give a straight side wall with a short tapered area just before the case head.
Bottle-neck cases like the .357 SIG are supposedly design to headspace off of the case mouth also, but don't in real life. An interesting article on this at the Real Guns website : http://www.realguns.com/archives/001.htm

Did you read this part of my post? "... .30-30 (rimmed) lever actions have extractors. .30-'06 (rimless) bolt actions have extractors. .223 (rimless) autos have extractors. Single shot .38-55 Ballards (rimmed) have extractors. NONE of them headspace on the extractor! ..." In all these examples, there is something the cartridge rests against when it goes bang, a bolt face, a breech block, etc., and each of them have an extractor. I won't take space quoting each different headspace method for each different case type, but suffice it to say, none of them headspace on "... what the case really is resting against when it goes bang.", nor the extractor.

Headspace is measured FROM the head of the case to some point in the chamber that is intended to "confine" the cartridge and "fix" it for firing. Let's say the headspace "ledge" wasn't part of a straight-walled auto pistol case (the chamber would need a taper at theat point into the rifling) and that the extractor face was the headspace point. Now think for a minute. How critical would the extractor face measurement be, from the breech face? Would an occasional cartridge slipped off the extractor and be sent into the chamber? If you would rather depend on the extractor holding the cartridge against the breech face, then be careful about some recommendations to customize the extraction angles on the extractor face, because that will cause some relaxation of extractor tension in battery. I think the extractor does play a part in keeping the case against the breech face. It's just not how you measure headspace.

After I reload a .45 ACP case several times, the case rim becomes a little battered and misshapen. I throw out a few that are really beat up, but the variations there are pretty large.

There is something in WESHOOT2's post that I may have read my own meaning into. And on re-reading it more carefully I see another take. <BLOCKQUOTE><font size="1" face="Verdana, Arial">quote:</font><HR>2) Auto cartridges headspace based on extractor tension holding the cartridge against the breech face.[/quote] That doesn't say that they headspace on the extractor, which I originally interpreted. But it does imply that the extractor keeps the cartridge from flying forward when chambering. Chris described that too. That much I agree with. But, sorry, that's not headspace.

I haven't read the American Handgunning article. I don't have a subscription. I'll look for it on the magazine racks.

As far as the .357 Sig goes, I'm gonna hang it out here and say I'll bet a dollar it headspaces on the shoulder. Most of the .40 brass used to make it would come out too short to headspace on the mouth. I don't know of a shouldered (bottle neck)round that doesn't headspace on the shoulder. Now I'll go to Chris's link and see if I owe you a dollar.

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Headspace is defined as the distance from the breech face to that part of the chamber that stops forward movement of the cartridge case. For straight wall rimless cases, that would be the distance to the chamber shoulder. For the .45 ACP, the SAAMI standard dimension for a maximum cartridge case is 0.898" and the length of a minimum chamber is the same.

Now, the chances of having a real world gun with a minimum chamber are slim, and it’s even more rare to find a case that long. Most of the time brass is at least 0.005" shorter. It would truly be a rare set of circumstances to have a case actually headspace on the case mouth. As a practical matter, the extractor usually determines headspace.
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